1. Field of the Invention
The present invention relates to a magnetic sensor, in particular a metallic surface identifying sensor, which detects an uneven shape on a surface of a metallic body.
The present invention also relates to a differential magnetism sensor apparatus in which the magnetic variation in a magnetizing coil caused by an object to be detected which generates a magnetic flux in a closed loop is amplified and output. In particular, the present invention relates to a signal processing method for a signal output from a differential detecting coil.
In addition, the present invention relates to a coin identifying apparatus and a magnetic sensor body. More specifically, the present invention relates to improvement in the configuration of an identifying sensor which identifies the authenticity of coins in a vending machine and the like.
Also, the present invention relates to a displacement sensor which detects a relative position in relation to an object to be detected.
Furthermore, the present invention relates to a proximity sensor which detects magnetically the location of an object to be detected without touching the object.
2. Related Art
A coin discriminating machine of an automatic vending machine which makes a distinction between the absence and presence of a coin and between types of coins and a card discriminating machine which makes a distinction between the absence and presence of a magnetic card and between types of magnetic cards both have a magnetism sensor apparatus on board. One type of magnetism sensor apparatus is a differential magnetism sensor apparatus which differentially detects a variation caused by an object to be detected in a magnetic flux which passes through a magnetizing coil, and is disclosed in Tokuhyo No. H7-506687 and Kokai No. H3-162688.
Tokkai S53-42985 discloses a magnetic sensor, in particular a metallic surface identifying sensor, which enables highly precise identification with a simple configuration by using a change in magnetic fluxes. Herein, as shown in FIG. 9, a pair of magnetic pole portions for detection 1 and 2 move while facing the surface to be identified 3a of metallic body 3 having an uneven shape wherein detecting coils 4 and 5 are wound around magnetic pole portions 1 and 2, respectively. Additionally, magnetizing coil 7 is wound around support magnetic pole portion 6 between the pair of detecting magnetic pole portions 1 and 2. When magnetic fluxes 1 and 2 are generated in detecting magnetic pole portions 1 and 2 by an electric flow in magnetizing coil 7, detection signals corresponding to magnetic fluxes 1 and 2 are sent out from detecting coils 4 and 5, respectively.
In the above case, eddy currents are generated on the surface to be identified 3a of metallic body 3 based on magnetic fluxes 1 and 2 such that the eddy currents restrict magnetic fluxes 1 and 2. The eddy currents correspond to the distance between the surface to be identified 3a as a front surface of metallic body 3 and magnetic pole portions for detection 1 and 2. In other words, when surface 3a is flat, both magnetic poles 1 and 2 are at the same distance from surface 3a such that the amounts of magnetic fluxes 1 and 2 to be restricted are identical. As a result, detecting coils 4 and 5 send out output signals of the same intensity. Therefore, a differential output by detecting coils 4 and 5 is maintained at zero.
In the case of the surface to be identified 3a of metallic body 3 having an uneven shape, the distance between magnetic pole portions for detection 1 and 2 and surface 3a continually increases or decreases according to the uneven shape on surface 3a during the shift. Consequently, eddy currents generated on surface 3a change according to a change in the distance. More specifically, when magnetic pole portion 1, which precedes to magnetic pole portion 2 on the right side in FIG. 1, faces convex portion 3b of surface 3a, the distance from magnetic pole portion 1 is small such that the eddy current becomes larger. As a result, the output from detecting coil 4 decreases. On the other hand, the following magnetic pole portion 2 on the left hand in the figure has a larger space between it and surface 3a wherein the eddy current is small such that detecting coil 5 generates a larger output. Consequently, the differential output from detecting coils 4 and 5 increases, for example, the output has a wave form including projecting portions A as shown in FIG. 10. Therefore, it is detected that surface 3a of metallic body 3 has convex portion 3b. 
In recent years, there has been a problem with forged foreign coins and counterfeit coins being frequently used with domestic vending machines and ticket machines.
Currently, the following means are employed solely or in combination to identify coins in vending machines, ticket machines and central processors depending on the required rate of identification:                1) a magnetic sensor detecting conductivity, mass, diameter and thickness of a metal piece as a difference in eddy current loss;        2) an optical sensor, such as a CCD, identifying the optical pattern of a coin; and        3) identifying the diameter and thickness by mechanically selecting the size.        
The conventional apparatus as described above has a simple configuration and is able to provide reliable detection outputs. However, the wave form of the detection outputs may differ from the actual shape of the surface.
For example, as shown in FIG. 1, when the summit of convex portion 3b on the surface to be identified 3a of metallic body 3 has an extended flat plane, both magnetic pole portion for detection 1, which is positioned on the right side in the figure, and the other magnetic pole portion 2, which follows magnetic pole 1 from the left side, can face the flat portion of convex portion 3b simultaneously. As a result, the distances from each of magnetic poles 1 and 2 to the surface become identical. Therefore, the sensor does not provide a differential output from detecting coils 4 and 5 although convex portion 3b exists thereat. As shown in FIG. 2(b), the differential output is zero such that the convex portion 3b cannot be detected.
However, qualities of the forged foreign coins and counterfeit coins are improved every year. Therefore, it is very difficult to prevent illegal use of those coins by using simple identification parameters such as the material, diameter and/or thickness.
Also, simultaneously verifying a section of a coin for more accurate identification data is required instead of the conventional macro identification of material, diameter and/or thickness.
In a coin transferring apparatus, the position of coin 102 tends to move (e.g. by about 0.3 mm) while being transferred, i.e., when the coin is falling with rotation in a vending machine or when the coin is transferred on belt 103 in a central processor. Therefore, a magnetic sensor using eddy current loss cannot identify any coin 102 having a diameter which is different from the original coin 102 by an amount smaller than the amount of the change in position.
The above discussed fluctuations in the position of the coin are within the acceptable limit as long as only domestic coins are subject of identification. However, identification may be impossible in the case of foreign coins which are similar in material, diameter and thickness.
The present invention intends to provide a magnetic sensor, in particular a metallic surface identifying sensor which can precisely identify the shape of a surface of a metallic body while maintaining a simple configuration. Also, the present invention intends to provide a magnetic sensor which individually detects information about metallic bodies such as coins, e.g., material, thickness and diameter, such that is precisely identifies the kind of metallic body to be detected or weather the metallic is authentic.
It is another purpose of the present invention to provide a differential magnetism sensor apparatus which gives a high precision of the detection even if outputs from differential detecting coils have a phase shift and which can cope with a high magnetizing frequency without an expensive differential amplifier.
Another purpose of the present invention is to provide a coin identifying apparatus and a magnetic sensor body which identify the authenticity of coins by improving identifying performance using the characteristics of the coins.
Yet another purpose of the present invention is to provide a coin identifying sensor which can accurately detect the diameter of a coin in spite of a change in the position of the coin.
Another purpose of the present invention is to provide a coin identifying sensor which accurately detects the thickness of a coin regardless of a change in the position of the coin.
The present invention also intends to provide a proximity sensor which shows a high sensitivity due to a large variation of the output of the detection corresponding to a variation of the distance from an object to be detected and also shows a good linearity of the output of the detection.
Another purpose of the present invention is to provide a proximity sensor which shows a good temperature characteristic of the output of the detection, the shape of which is thin.